He discusses the genesis and nature of silver ores, the dry refining process: smelting of silver ores and its impact on the environment, the wet refining process: the chemistry of the patio process
, the physical infrastructure of the patio process
, the Hacienda Santa Maria de Regla, the patio process
and smelting at Regla, the economics of refining silver, and the environmental impact of silver refining: a shift of paradigm.
He investigated the patio process as it was being practiced in Mexico with mercury from Almaden, and then demonstrated the process to the Peruvian Viceroy.
Before the advent of the patio process, these ores were simply roasted out of the veins, then reduced in crude furnaces: one observer wrote that "the Peruvians get the silver by burning the hill, and, as the sulfur stone burns, the silver falls in lumps" (Rickard, 1932).
Before the advent of the patio process, the Spanish in South America borrowed their ore-smelting technology from the Incas.
A Spaniard from Seville, Medina may have known Agricola's De Re Metallica, which describes a similar method, but it is clear that he worked out the patio process at the Pachuca mines, in Hidalgo, New Spain (Dahlgren, 1883; Graham, 1907).
The success of the patio process meant that mining no longer was confined to near-surface bonanza ores; some lower-grade ores could also be worked economically.
The Patio Process is often mentioned but seldomly described in the metallurgical literature.
The patio process was not too well suited for northern climates where freezing was encountered and people were in a hurry.
The intent of this article has been to describe the ancient silver recovery methods, especially the Patio Process.
Few textbooks on metallurgy give the chemistry of the Patio Process.
Van Nostrand, 1954 (This is the reference containing the chemistry of the Patio Process.
The patio process
for silver recovery originated in Mexico [ednote--the little-known chemistry of the patio process
is described in a special report on the older processes for silver recovery in next issue of E&MJ].